Device comprising a rotor and a magnetic suspension bearing for the contactless bearing of the rotor

ABSTRACT

The device comprises a) a rotor which can rotate or rotates about a rotational axis and b) at least one magnetic suspension bearing, in which the rotor can be or is mounted in a contactless manner and which comprises at least one super-conductive structure in addition to several permanent magnets, and c) a cooling device comprising at least one refrigeration head for cooling the super-conductive structure of the or each magnetic suspension bearing, whereby d) the rotor and each magnetic suspension bearing are arranged in a common gas chamber, which is surrounded by a gas-proof wall. The advantage of the device is that ice is prevented from forming on the magnetic suspension bearing.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based on and hereby claims priority to PCTApplication No. PCT/DE01/03655 filed on 21 Sep. 2001 and GermanApplication No. 100 49 821.3 filed on 9 Oct. 2000, the contents of whichare hereby incorporated by reference.

BACKGROUND OF THE INVENTION

The invention relates to a device having at least one rotor whichrotates or can rotate about a rotation axis, and having at least onemagnetic bearing in which the rotor is borne or can be borne in acontactless manner.

U.S. Pat. No. 5,482,919 A discloses a device which has a rotor which canrotate about a rotation axis and has at least one superconductingwinding (field coil) for an electric motor, and has a cryogenic coolerfor cooling the superconducting winding. The superconducting winding maybe formed from a known, metallic superconductor material(low-temperature superconductor) with a low critical temperature ofT_(c), below 35 K, such as a niobium-tin alloy or a ceramic metal-oxidesuperconductor material (high-temperature superconductor) with a highcritical temperature T_(c) above 35 K, such as bismuth strontium calciumcopper oxide, an yttrium barium copper oxide or a mercury or thalliumcompound. The cryogenic cooler makes use of rapid expansion of a workingfluid (which is compressed by a compressor) such as helium, neon,nitrogen, hydrogen or oxygen for cooling in thermodynamic cycles(processes) such as a Gifford-McMahon cycle, a Stirling cycle or a pulsetube cycle. The superconducting winding is thermally conductivelyconnected to a cold head, which rotates with the rotor, of the cryogeniccooler via two or more annular supporting elements composed of amaterial with a high thermal conductivity coefficient, and which areconnected via heat pipes or thermally conductive rods. In this way, heatis dissipated from the superconducting winding by thermal conductionthrough a solid body to the cold head. There is no need for a liquidcoolant such as liquid helium or liquid nitrogen in this known coolingsystem, so that there is also no influence on the rotation of the rotorfrom a cold liquid. The compressor of the cryogenic cooler can rotatewith the rotor or may be in a fixed position with respect to the rotor,and may be connected to the cold head via a rotating coupling. U.S. Pat.No. 5,482,919 A states nothing more with regard to the bearing of therotor.

Magnetic bearings are generally known for bearings for rotors, and allowthe rotors to be borne in a contactless bearing, which is thus free ofwear. Both active magnetic bearings with electromagnets and positioncontrol as well as passive magnetic bearings with automatic positionstabilization are known.

DE 44 36 831 C2 discloses a passive magnetic bearing for bearing a rotorshaft with respect to a stator, which has a first bearing part which isconnected to the rotor shaft, and a second bearing part which isarranged on the stator and surrounds the first bearing part. One of thetwo bearing parts has a high-temperature superconductor. The otherbearing part has an arrangement of permanent-magnet elements arrangedalongside one another and composed of a neodymium (Nd), Iron (Fe) boron(B) alloy or of a samarium (Sm) cobalt (Co) alloy. Adjacentpermanent-magnet elements are magnetized with opposite polarity to oneanother. When a position change occurs, the permanent-magnet elementsinduce shielding currents in the superconductor, as a result of fieldchanges. The resultant forces may be repulsive or attractive, but arealways directed such that they counteract the deflection from thenominal position. In contrast to known active magnetic bearings, aninherently stable bearing can be achieved in this case, and there is noneed for a complex control system that is subject to defects. Theintermediate spaces between in each case two permanent-magnet elementsare filled with ferromagnetic material in order to concentrate themagnetic flux, which emerges from the permanent-magnet elements, on theside facing the other bearing part. This results in a high level ofbearing stiffness (stability, robustness). The permanent-magnet elementstogether with the ferromagnetic intermediate elements may be arrangedaxially with respect to the rotor shaft axis one behind the other in theform of thin rings, or else may be axially elongated and arranged onebehind the other in the circumferential direction.

In a refinement of this known magnetic bearing, the permanent magnetsare provided in a hollow-cylindrical arrangement on the inner bearingpart, and the superconductor is arranged as a hollow-cylindricalstructure on the inside of a hollow-cylindrical supporting body for theouter bearing part. Cooling channels are formed in the supporting bodyfor passing liquid nitrogen through in order to cool the superconductor.

In another refinement according to DE 44 36 831 C2, the high-temperaturesuperconductor on the inner bearing part is arranged on the rotor shaft,with a coolant channel being provided for the liquid nitrogen in therotor shaft, in order to cool the high-temperature superconductor. Thisembodiment with a cold rotor body is proposed as part of a generator orof a motor with a cryogenic normally conductive or superconductingwinding.

The document U.S. Pat. No. 5,214,981 A discloses a device for storingenergy. This device has a rotating flywheel which has permanent magnets(which interact with stationary electromagnets) on its circumference forpower transmission. The flywheel is borne in each case one magneticbearing on opposite sides via two rotor shafts. In one embodiment (FIG.1), one or more permanent magnets are provided in a cylindricalarrangement at each of the ends of the two rotor shafts. These endsproject as first bearing parts into in each case one superconductor, inthe form of a pot, as the second bearing part for the respectivemagnetic bearing. For cooling, the superconductors are each arranged ina cold bath of liquid nitrogen. In another embodiment (FIG. 3), eachrotor shaft has a recess as the first magnetic bearing part on its endface facing away from the flywheel, with this recess being clad with asuperconductor. The superconductor is cooled exclusively by the thermalradiation from the superconductor to the vacuum vessel, which is kept ina liquid bath filled with liquid nitrogen. Furthermore, the magneticbearings have cylindrical second bearing parts, whose ends project intothe recesses in the rotor shafts and have one or more permanent magnetsin a cylindrical arrangement. The flywheel is enclosed together with thetwo magnetic bearings in a vacuum vessel which is evacuated to apressure of less than 10⁻⁴ Torr, in order to avoid friction of therotating parts and the energy losses associated with such friction. Thebearing gaps of the two magnetic bearings form continuous connectionsbetween the adjacent evacuated areas of the vacuum vessel.

JP 04370417 A and the associated abstract from Patent Abstracts of Japandisclose a further device for storing energy by a flywheel which isborne in two magnetic bearings and is arranged together with themagnetic bearings in a common evacuated vacuum chamber. Each magneticbearing has a central permanent-magnet ring on the flywheel and twosuperconductor rings at an axial distance from it, which are arranged onstationary supporting disks, through which liquid coolant flows.

Finally, DE 197 10 501 A1 discloses an electrical machine having astator with a polyphase winding for producing a rotating magnetic field,and with a rotor which rotates with the rotating field. The stator has amagnetic return path yoke, which forms a housing for the rotor. Therotor has a shaft which is passed through an opening, which is notsealed, in the housing and magnetic return path yoke. The rotor iscomposed entirely, or at least on its outside, of a high-temperaturesuperconductor. Magnetic bearings for contactless bearing of the rotorare formed by the superconductor and by annular permanent magnets whichare provided at two points. In order to cool the superconductor on therotor, the entire machine is designed to have a small physical size andis operated completely in a cryogenic bath formed from liquid nitrogen.

Owing to the contactless bearing, the known magnetic bearings alwayshave a continuous bearing gap, and gas and vapor can thus pass throughthem between the two sides which are connected by the bearing gap.Environmental air and moisture contained in it can thus enter thebearing gap, or can reach the rotor through the bearing gap. Thisresults in the risk of the air humidity freezing on the cold componentsof the magnetic bearing or else of the rotor, if this is cooled, withsuch icing resulting in a restriction to operation, or even in damage tothe magnetic bearing. Furthermore, the cooling processes with liquidcoolant (cryogenic medium), in general liquid nitrogen, which are usedexclusively for the superconductors of the described magnetic bearingaccording to the related art, are generally also subject to sealingproblems in the region of the sensitive magnetic bearings, in additionto the problem of any moisture that has entered freezing on thecryogenic medium supply lines that are required, once again increasingthe risk of icing or of other malfunctions of the magnetic bearing.

SUMMARY OF THE INVENTION

One aspect of the invention is based on the object of protecting themagnetic bearing or magnetic bearings for bearing of a rotor againstsuch adverse effects on operation or damage.

The device accordingly has a rotor which rotates or can rotate about arotation axis and at least one magnetic bearing, in which the rotor isborne or can be borne in a contactless manner (or without wear), andwhich has at least one superconductor (or: a superconducting structure).

The rotor is arranged together with the associated magnetic bearing orbearings in a common gas area (or gas-filled chamber), which issurrounded by a gastight wall. The rotor and magnetic bearings are thus,in other words, located in the same gas atmosphere, which is separatedand shielded from the environmental air by the wall through which gascannot pass. These measures result in the bearing gap of each magneticbearing being filled with the gas with which the gas area is filled, andbeing protected by the gas area wall against the ingress ofenvironmental moisture. Furthermore, pressure fluctuations, for exampleas a result of gas losses, can be tolerated within certain limits, sincethey affect all the components in the gas area in the same way.

As a further measure, a cooling device having at least one cold head,which is thermally coupled to the superconductor and dissipates heatfrom the superconductor mainly by thermal conduction as the heattransfer mechanism, is now provided for cooling the superconductor ofthe magnetic bearing or of each magnetic bearing. The use, as proposed,of a cold head (which in principle is known per se) for indirect coolingof the magnetic bearing is a considerably simpler solution in terms ofdesign and handling than the direct cooling, as provided in the relatedart, via a liquid cooling medium. A cold head can easily be fitted tothe magnetic bearing as a connecting piece for heat transmission.Furthermore, the use of one or more cold heads ensures deliberatecooling of the superconductor in the magnetic bearing and avoids theproblems of the emergence (which can never entirely be avoided) ofcryogenic liquid and the uncontrolled thermal conditions that resultfrom this, with the risk of icing of the magnetic bearings as a resultof freezing of residual moisture in the gas atmosphere or of moisturecontained in the evaporated cryogenic medium.

The cooling device for cooling the cold head and hence for indirectcooling of the magnetic bearing or bearings preferably has a cryogeniccooler system which is operated in particular electrically and does notrequire the handling of cryogenic liquid gases in conjunction with thecold head. Different cold heads may in each case be connected to adedicated cryogenic coolant, or else in any desired combinations toshared cryogenic coolers. Each cold head is preferably guided from theoutside in a direction running essentially at right angles to therotation axis to the superconducting structure of the magnetic bearing.

The magnetic bearing or bearings of the device generally has or have atleast one inner bearing part and at least one outer bearing part, withthe outer bearing part surrounding the inner bearing part and with abearing gap, which runs around the rotation axis, being formed betweenthe two bearing parts, and one of the two bearing parts is connected orcan be connected to the rotor, in particular to its rotor shaft.

One of the two bearing parts of the magnetic bearing now preferably hasat least one permanent magnet, while the other bearing part has thesuperconducting structure, which interact electromagnetically (byinduction) with the permanent magnet or permanent magnets such that thebearing gap between the inner bearing part and the outer bearing part isformed or maintained. Where there are two or more permanent magnets,these are generally arranged alongside one another, in particularaxially one behind the other with respect to the rotation axis andpreferably in each case surround the rotation axis in a shape that isclosed all round, in particular in the form of a ring, or else alongsideone another in an arrangement which surrounds the rotation axis. Thepermanent magnet or magnets in one advantageous refinement surrounds orsurround the rotation axis in a closed (all round) form, preferably inthe form of a ring. The ring cross section may in this case inparticular be circular, in the form of a disk or rectangular,corresponding to a hollow-cylindrical or toroidal ring shape. The ringlongitudinal section at right angles to the rotation axis may thus, inparticular, be in the form of a circular ring. Immediately adjacentpermanent magnets are preferably magnetized with essentially oppositepolarity to one another, at least on average, over domains which may bepresent.

One advantageous development of the magnetic bearing is characterized inthat a flux concentrating element is in each case arranged between atleast two of the permanent magnets, and/or a flux concentrating elementis in each case arranged on the outside of the outer permanent magnetsin the axial direction. Each flux concentrating element is used forconducting the magnetic flux of the permanent magnets and, in general,also for concentrating and amplifying it in the bearing gap and, forthis purpose, is at least partially composed of a magnetically permeablematerial, in particular of a ferromagnetic material, for example iron(Fe).

The superconducting structure preferably surrounds the rotating axis ina closed form, in particular in the form of a ring, and/or essentiallyhas a cylindrical shape, at least on the side facing the bearing gap.Furthermore, it is advantageous for the superconducting structure to bearranged on the side of the bearing part facing the bearing gap, inorder to achieve good coupling efficiency.

In general, at least one cold head is in each case provided for eachmagnetic bearing, for cooling the superconducting structures and,expediently, the permanent magnets as well, in order to achieve ahighercoercivity field strength.

The bearing gap of at least one of the contactless magnetic bearings isnow preferably connected to the gas area and allows gas to be exchanged.In consequence, the bearing gap is located in the same gas atmosphere asthat found in the gas area.

In general, the wall of the gas area is in a fixed position with respectto the rotor, that is to say its position relative to the rotation axisof the rotor remains unchanged during rotation of the rotor.

The rotor is preferably borne in the magnetic bearing via a rotor shaftwhich is connected or can be connected to the rotor. The rotor shaft ispreferably passed to the outside through an opening, which is sealed bya rotation seal, in the wall of the gas area.

In one particularly advantageous embodiment of the device, the rotor isborne in at least two magnetic bearings, preferably via in each case onerotor shaft, which magnetic bearings are arranged on axially oppositesides of the rotor with respect to the rotation axis. The rotor is thusheld in bearings on both sides and thus in a particularly robust manner.

One advantageous development of the rotor is characterized by at leastone winding (coil) which generally runs around the rotation axis and ispreferably formed by a superconductor.

Any low-temperature superconductors or high-temperature superconductorsmay be used as superconductors for the magnetic bearings and/or for thewinding on the rotor. The superconductor may be a traditionallow-temperature superconductor with a critical temperature up to 35 K,for example a metallic alloy such as a niobium tin alloy, or preferablya high-temperature superconductor with a critical temperature above 35K, preferably above 77 K (i.e. the boiling point of nitrogen),preferably a metal-oxide or ceramic high-temperature superconductor suchas bismuth strontium calcium copper oxide, yttrium barium copper oxideor a compound of mercury or thallium. The higher the criticaltemperature of the superconductor, the less energy is required forcooling.

Since high-temperature superconductors are, in particular,self-supporting only to a restricted extent, one advantageousdevelopment allows the superconducting structure of the magnetic bearingor the superconducting winding of the rotor to be arranged on or in asupport or winding support. In order to cool the superconductor, thesupport or winding support preferably has a high thermal conductivity,for example being formed from metal.

In one particularly advantageous embodiment, the winding support of therotor has a cavity (internal area) which extends axially with respect tothe rotation axis. The winding can now advantageously be cooled in aspace-saving manner via this cavity, in that a heat transmission unit inthe cavity or on the cavity is thermally coupled to the winding support,preferably via a contact gas in the cavity.

The heat transmission unit is now preferably thermally coupled or can bethermally coupled to a cooling device for the rotor. This cooling devicemay be designed in a manner known per se, for example according to theinitially cited U.S. Pat. No. 5,482,919 A, whose entire disclosurecontent is also included in the present application. The cooling deviceand/or heat transmission unit for the rotor may also operate with aliquid coolant such as liquid helium or liquid nitrogen, or else mayhave a cryogenic cooler system with at least one cold head, in the sameway as the cooling system for the magnetic bearing.

According to one particular embodiment, the heat transmission unit has apreferably cylindrical heat transmission body which projects into thecavity in the winding support and between which and the winding supportan intermediate gap is formed, which runs around the rotation axis andis filled with a contact gas. The heat transmission from the or coolingof the winding now takes place essentially by thermal conduction throughthe solid body and via the contact gas.

However, alternatively or additionally, cyclic vaporization andcondensation of a heat transport gas, with appropriately chosenvaporization enthalpy, can also be used as the heat transport mechanism.The heat transmission unit may then, in particular, comprise a heatpipe.

In an embodiment which makes use of both the thermal transportmechanisms of thermal conduction and vaporization, the cavity in thewinding support is at least partially filled with the heat transportgas, so that the heat transport gas is also used as the thermallyconductive contact gas.

The cavity in the winding support and the intermediate gap between theheat transport body and the winding support can also be connected to thegas area in a manner which allows gas to be exchanged. This then resultsin a standard gas atmosphere inside and outside the rotor, and there isno longer any need to take any special measures in order to seal thesegas areas.

The contactless arrangement of the heat transmission unit in the windingsupport is particularly advantageous when the two components areintended to be mechanically decoupled from one another, that is to saythe heat transmission unit is intended to be fixed during rotation ofthe rotor. Such a fixed configuration of the heat transmission unit,which does not rotate with the rotor, and possibly of the connected coldhead is expedient since there is no need to seal any rotating parts ofthe cooling system with respect to one another.

In one special physical development, at least one rotor shaft, which isborne in the associated magnetic bearing, is in the form of a hollowshaft. The hollow shaft can now at least partially accommodate the heattransmission unit and/or a connection between the gas area and aninternal area of the rotor, in particular the cavity in the windingsupport

In order to protect the winding, it is preferably arranged in aninternal area of a container in the rotor, which is preferably evacuatedand is sealed from the rest of the gas area and from the cavity in thewinding support.

The gas area of the device, in which the rotor and the magnetic bearingare arranged, is generally filled with a gas or a gas mixture which isused for thermal conduction for cooling of those components which needto be cooled and for this purpose makes contact with them and istherefore also referred to as the contact gas. This gas generallyremains in the gas area throughout the operating life of the device. Thecontact gas is therefore in one advantageous embodiment an inert gas ora mixture of inert gases, with helium or neon being preferable, althoughnitrogen can be used for correspondingly high operating temperatures.Furthermore, in principle, hydrogen or oxygen are also suitable,although their handling is somewhat more problematic.

The gas with which the gas area is filled preferably contains virtuallyno water, or contains less than a critical amount of water, so that itis impossible for water to freeze on cold parts in the gas area. Forthis purpose, the gas is prepared with an appropriate purity, and/or isdried.

The gas pressure of the gas in the gas area in one advantageousembodiment is preferably at least as high as, and preferably higherthan, the gas pressure in the outer area surrounding the wall of the gasarea, in general atmospheric pressure. Even in the event of sealingproblems or leakages in the area of the gas area wall, this reliablyprevents the ingress of moist air and the possibility of ice beingformed in consequence in the cold area.

The device is preferably used for electrical machines such as motors andgenerators.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and advantages of the present invention willbecome more apparent and more readily appreciated from the followingdescription of the preferred embodiments, taken in conjunction with theaccompanying drawings of which:

FIG. 1 shows a device having a rotor, which is borne in two magneticbearings, in a longitudinal section on a plane containing the rotationaxis of the rotor,

FIG. 2 shows an embodiment of a magnetic bearing of the device, in aperspective and partially sectioned view,

FIG. 3 shows another embodiment of a magnetic bearing of the device, ina longitudinal section,

FIG. 4 shows a further embodiment of a magnetic bearing of the device,in a cross section in a plane at right angles to the rotation axis, and

FIG. 5 shows a device having a rotor, which is borne in two magneticbearings, and having a heat pipe, in a longitudinal section, in eachcase illustrated schematically. Mutually corresponding parts areprovided with the same reference symbols in FIGS. 1 to 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings, wherein like reference numerals refer to like elementsthroughout.

FIG. 1 shows a device having a rotor 20 which is borne such that it canrotate in magnetic bearings 2 and 3 positioned respectively on bothsides (end faces) axially with respect to its rotation axis A. For thispurpose, a first rotor shaft, which is in the form of a hollow shaft(neck tube) 34, is formed or mounted on the rotor 20 on the left-handside in FIG. 1, and is borne in a contactless manner in the magneticbearing 2. In the illustrated embodiment, the hollow shaft 34 also has alength compensator 36, in particular an expanding bellows, for lengthcompensation. A second rotor shaft 4 (which is, for example, solid), isformed or mounted on the rotor 20 on the opposite side, on the right inFIG. 1, and is borne in a contactless manner in the magnetic bearing 3.Both shafts, the hollow shaft 34 and the rotor shaft 4, are preferablyrotationally symmetrical with respect to the rotation axis A, inparticular being hollow-cylindrical or cylindrical, or else at leastslightly conical.

Each of the magnetic bearings 2 and 3, which are preferably essentiallythe same, has a bearing inner part 5, which is connected to theassociated hollow shaft 34 or rotor shaft 4, and a bearing outer part11, which surrounds the bearing inner part 5 forming a bearing gap 10.The bearing inner part 5 has two or more permanent magnets, which arenot annotated in any more detail in FIG. 1, on its outside facing thebearing gap 10. Opposite the permanent magnets, the bearing outer part11 has a superconducting structure 12 on its inside facing the bearinggap 10, and this is supported on the outside on a supporting body 13.The superconducting structure 12 makes contact with a respective coldhead 22 or 23, which projects through the supporting body 13 from theoutside, for cooling. The design of the magnetic bearings 2 and 3 willbe described with reference to the detailed FIGS. 2 to 4. First of all,the further parts of the device shown in FIG. 1 will now be described inmore detail.

The rotor 20 has at least one winding (coil) 25, which is composed of asuperconducting material and has one or more turns which run around therotation axis A, preferably with essentially the same radius. Thewinding 25 is supported on or in a winding support 26, which surroundsthe rotation axis A in the form of a hollow body, preferably with ahollow-cylindrical shape. The winding support 26 is composed of athermally highly conductive material such as a metal.

A central cavity 30, through which the rotation axis A runs, is formedin the interior of the winding support 26. On the side pointing towardthe rotor shaft 4, the cavity 30 is closed by the winding support 26,while it is open on the side pointing toward the hollow shaft 34. Onthis side, a cylindrical heat transmission body 35 projects through theopening in the winding support 26 into the cavity 30, and extends to apoint shortly before its end on the opposite side. The heat transmissionbody 35 is composed of a thermally highly conductive material, forexample of a metal such as aluminum or copper, or, in order to avoidEddy currents, alternatively of a dielectric, thermally conductivematerial such as a ceramic, for example aluminum oxide (Al₂O₃) oraluminum nitride (AlN), or of monocrystalline sapphire.

An intermediate space 39 is formed all round between the heattransmission body 35 and the inner surface of the winding support 26.Adjacent to the winding support 26, the heat transmission body 35 ispassed outward through a central cavity in the suspension element 48located on this side, into the cavity of the hollow shaft 34, in eachcase forming an intermediate space 38 or 37. The intermediate spaces(gaps) 37 to the hollow shaft 34, 38 to the suspension element 48 and 39to the winding support 26 mean that the heat transmission body 35 can bearranged in a fixed position overall with respect to these rotatingparts and the respective rotor 20, that is to say not rotating withthem.

A contact gas is introduced at least into the intermediate space 39between the heat transmission body 35 and the winding support 26, andprovides thermal coupling between the winding support 26 and the heattransmission body 35. The intermediate spaces 39, 38 and 37 arepreferably connected to one another, as shown, so that the contact gasis located in all the intermediate spaces 37 to 39. Helium or neon ispreferably provided as the contact gas.

At its end facing away from the end that is located in the cavity 30 inthe winding support 26, the heat transmission body 35 is thermallycoupled to one end of a cold head 24, which extends into the hollowshaft 34 from the opposite side, axially with respect to the rotationaxis A. The heat transmission body 35 is cooled via the cold head 24,which is connected to a cooling device which is not illustrated in anyfurther detail, in particular to a cryogenic cooler that is known perse. In consequence, the winding support 26 is also cooled indirectly bythermal conduction via the contact gas and, finally, the superconductingwinding 25, which actually needs to be cooled, is cooled by the goodthermal conduction capability of the winding support 26. This thereforeprovides cooling for a rotating part, the winding 25, via a stationarypart, the heat transmission body 35.

The winding support 26 together with the winding 25 is arranged in theinternal area of a container 21 and is suspended on both end faces onthe wall of the container 21, via in each case one suspension element 48with a metal sleeve and a hollow core composed of thermally insulatingmaterial. On the outside (outer surface), the winding support 26 is at adistance from the wall of the container 21. The intermediate space whichis formed in the internal area of the container 21 between the windingsupport 26 and the container wall is preferably evacuated to a desiredresidual pressure, in order to ensure that the winding support 26 isthermally insulated as well as possible from the outside. This evacuatedarea in the container 21 is separated in a gastight manner by thewinding support 26 itself and by the two suspension elements 48 from theIntermediate spaces 39 and 38 around the heat transmission body 35.

The rotor 20 together with the two rotor shafts 34 and 4 and the twomagnetic bearings 2 and 3 are now jointly arranged in a gas area 60,which is surrounded in a gastight manner by a wall 61 through which gascannot pass. This gas area 60 is filled with a gas 50 with apredetermined composition, in particular a chemically resistant (inert)gas such as neon or helium, or a mixture of them.

The hollow shaft 34 on the rotor 20 now preferably opens, asillustrated, at the end facing the rotor 20 into the gas area 60, sothat a gas connection is formed between the external region of the gasarea 60 and the intermediate spaces 37, 38 and 39. Furthermore, thebearing gaps 10 of the magnetic bearings 2 and 3 are also each open onboth sides to the gas area 60. The intermediate spaces 37, 38 and 39,the bearing gaps 10 and the other gas area 60 are thus filled with thesame gas 50. The gas 50 thus at the same time forms the contact gas forcooling the winding 25 and acts as a protective gas for the magneticbearings 2 and 3, thus carrying out a plurality of functions.

The cold head 24 for the winding 2 and the cold heads 22 and 23 for themagnetic bearings 2 and 3 are passed through the wall 61 of the gas area60, and are expediently also held or secured on the wall 61 of the gasarea 60. The bearing outer parts 11 of the magnetic bearings 2 and 3 arealso mounted on the wall 61, via holding elements 52 and 53,respectively. The wall 61 and the components which are mounted on it arepreferably fixed in position and do not rotate with the rotor 20.

The rotor shaft 4, which is mounted in the magnetic bearing 3, passesthrough an opening in that end face of the wall 61 of the gas area 60which is opposite the cold head 24. This passage for the rotor shaft 4through the wall 61 of the gas area 60 is sealed from the inside by anexternally located rotating seal 40, in particular a sliding ring orretaining ring seal, a radial shaft seal, a gland seal or a ferro-fluidseal against the ingress of air from the outside or against the contactgas 50 escaping.

The pressure of the gas 50 in the gas area 60 is generally set to atleast atmospheric pressure (approximately 1 bar) and preferably to apressure which is greater than atmospheric pressure. This results in adevice which is insensitive to pressure fluctuations and is particularlywell protected against air moisture entering from the outside, andagainst leakage.

The gas 50 is generally at least approximately at the ambienttemperature in the region of the gas area 60 (outer area) that islocated outside the rotor 20 and outside the magnetic bearings 2 and 3.The temperature gradient between the cryogenic temperatures inside therotor 20 and inside the magnetic bearings 2 and 3, on the one hand, andthe considerably higher temperature in the external area of the gas area60 on the other hand is maintained in relatively narrow gaps, which arefilled with the gas 50 and are formed by the intermediate spaces 37 to39 and the bearing gaps 10. In order to produce the temperature gradientin the gas gap which is formed from the intermediate space 37 betweenthe hollow shaft 34 and the cold head 24, annular brushes, which are notshown, for example three to five brushes, can also be arranged staggeredin the axial direction in the gas gap, in order to avoid or to reducethe introduction of heat by convection.

Outside the container 21, the winding 26 surrounds a stator winding 45on a stator support 46. The stator winding 45 and stator support 46together with an external housing which encloses them both form thestator of an electric motor, in particular of a synchronous motor, orgenerator. These are the preferred applications, but not the onlyapplications, of the device according to the invention.

FIG. 2 shows a magnetic bearing which may be used in particular as themagnetic bearing 3 shown in FIG. 1, illustrated in an enlarged,perspective form. The bearing inner part 5 is provided with two or more,for example six, permanent-magnet elements (permanent magnets) 6 a to 6f in the form of annular disks. These permanent-magnet elements 6 a to 6f are in each case polarized such that, seen axially, that is to say inthe direction of the rotation axis A, the polarization alternates fromone element to the next. The individual polarization directions areindicated by lines 7 with arrows on them in the figure. Elements(intermediate elements) 8 a to 8 e composed of a ferromagnetic material,for example iron, and in the form of annular disks are arranged betweenthe permanent-magnet elements 6 a to 6 f. Furthermore, ferromagneticelements 8 f and 8 g, which correspond to the elements 8 a to 8 e, areprovided on the end-face outer surfaces of the outer permanent-magnetelements 6 a to 6 f. The ferromagnetic material of these ferromagneticelements 8 a to 8 g is used to concentrate and homogenize the magneticflux on the cylindrical outer surface of the bearing inner part 5, andthus increases the supporting force of the bearing 2. At the same time,the ferromagnetic elements 8 a to 8 g also mechanically reinforce thebearing inner part 5 with the permanent-magnet elements 6 a to 6 f,which are generally composed of a brittle material. All the elements 6 ato 6 f and 8 a to 8 g are mounted in the form of a stack, axially onebehind the other, on the rotor shaft 4. The rotor shaft 4 isadvantageously composed of a nonmagnetic material, or material whichcannot be magnetized, for example of a special steel.

The bearing inner part 5 is surrounded by a hollow-cylindrical,fixed-position bearing outer part 11, separated by a bearing gap 10. Thegap width (radial size) w of the bearing gap 10 between the bearinginner part 5 and the bearing outer part 11 is preferably in the sameorder of magnitude as the axial thickness d2 of the ferromagneticintermediate elements 8 a to 8 g, and is typically between 0.1 mm and 5mm, and preferably between 0.3 mm and 1.5 mm.

The bearing outer part 11, which forms a stator, has a superconductingstructure 12 on its inner face, facing the bearing inner part 5, whichsuperconducting structure 12 is supported externally on a supportingbody 13 which is composed, for example, of metal, in particular copper(Cu). Any known superconductor material, in particular texturedYBa₂Cu₃O_(7-x), may be used as the superconducting material for thesuperconducting structure 12. The crystalline a-b planes of at least alarge proportion of the superconductor material are in this caseadvantageously aligned essentially parallel to the outer surface of thebearing inner part 5. The mean grain size (grain diameter) of thecrystallites (grains) of the superconductor should in this case belarger than the axial thickness d1 of the permanent-magnet elements 6 ato 6 f, with the grain size being considered in the crystalline a-bplanes.

The magnetic flux which is caused by adjacent permanent-magnet elements(for example 6 d, 6 e) on the bearing inner part 5 is largelyconcentrated in the shared ferromagnetic intermediate element (8 d) andthus emerges with a high flux density via this intermediate element intothe bearing gap 10. In the bearing gap 10, the flux path is closed tothe respectively adjacent intermediate elements (8 c and 8 e,respectively). The magnetic flux which is produced by the individualmagnetic poles induces corresponding currents, which in turn result inmagnetic coupling or negative feedback, in the fixed-positionsuperconducting structure 12 which surrounds the bearing inner part 5and bounds the bearing gap 10. The magnetic flux path in the area of thenonmagnetic material of the rotor shaft 4 is closed on the side of therotor shaft 4. This advantageously avoids any magnetic short-circuitthere, which would lead to a reduction in the magnetic flux emerginginto the bearing gap 10.

The permanently magnetic material of the elements 6 a to 6 f should havea maximum energy product (B*H)_(max) of at least 20 MGOe, in order toapply the necessary bearing forces and provide the necessary bearingrobustness. Suitable materials with such a high energy product are inparticular a neodymium (Nd) iron (Fe) boron (B) alloy, or a samarium(Sm) cobalt (Co) alloy. The permanently magnetic material may also, ifrequired, be cooled in order to increase its coercivity field strength.

Outside the region of the bearing inner part 5, the magnetic bearing 3has a holding and centering apparatus 15 which can be lowered andabsorbs the bearing force when at rest, when the superconductingmaterial is above its operating temperature.

At the same time, the bearing position is centered axially and laterallyby a groove 17 in the rotor shaft 4 and by a rest 18, in the form of ablade, on the device 15. Electromagnetic induction results inelectromagnetic forces between the bearing inner part 5 and the bearingouter part 11 (stator) which surrounds it, and these electromagneticforces act counter to the direction of movement and lead to the bearinginner part 5 and the rotor shaft 4 floating freely approximately in thecenter of the bearing gap 10. This type of bearing makes it possible toachieve bearing pressures of up to 10 bar and considerable bearingstiffness against movements of the rotor shaft 4 and of the rotor 20 inthe radial and axial directions.

FIG. 3 shows a further embodiment of a magnetic bearing, which isexpediently used as the magnetic bearing 3 (or 2) as shown in FIG. 1. Astack of permanent-magnet elements 6 j alternating with ferromagneticelements 8 i is once again provided on the bearing inner part 5. Thisstack of elements 6 j and 8 i is mounted, as shown in FIG. 3, on asupporting body 54, which is kept at a distance from the rotor shaft 4by holding disks 57 which are composed of thermally insulating,mechanically robust material, for example of a fiber-reinforced, inparticular glass-fiber-reinforced, plastic, and with a thermalinsulation material 55 located in between. The bearing outer part 11likewise once again has a superconducting structure 12 and a supportingbody 13 for the superconducting structure 12.

A cold head 23 is once again connected to the supporting body 13,running vertically from the outside to the inside, and is thus thermallycoupled to it, and rests on or is attached to an outer sleeve 19 of themagnetic bearing 3. The supporting body 13 is connected to the outersleeve 19 via holding disks 57 and thermal insulation material 56arranged in between.

In the particular refinement shown in FIG. 3, a thermal insulation body14 or 14′, which points inward to the rotor shaft 4 from the outsidesleeve 19, is now in each case mounted in front of the end faces of thesuperconducting structure 12 with the supporting body 13 and the innerbearing part 5 with the magnet stack on both sides, axially with respectto the rotation axis. A first bearing gap element 41, which runsparallel to the rotation axis A, is formed between the thermalinsulation body 14 and the rotation shaft 4. A second bearing gapelement 42, which runs at right angles to the rotation axis A, is formedbetween the bearing inner part 5 and a side of the thermal insulationbody 14 which faces inward toward the bearing inner part 5. A thirdbearing gap element 43, which runs at right angles to the rotation axisA, is formed in an analogous manner between the bearing inner part 5 anda side of the further thermal insulation body 14′ which faces inwardtoward the bearing inner part 5, and a further, fourth bearing gapelement 44, which runs parallel to the rotation axis A once again, isformed between the rotation shaft 4 and the thermal insulation body 14′.A gas passage through the magnetic bearing 3 for the gas 50 is formed bythe first bearing gap element 41, the second bearing gap element, thebearing gap 10, the third bearing gap element 43 and the fourth bearinggap element 44 that are connected in series. The advantage of thisspecific embodiment of the bearing gaps is that the first bearing gapelement 41 and the fourth bearing gap element 44, which are located inthe comparatively warm end regions of the magnetic bearing 3, arelocated closer to the rotation axis A than the bearing gap 10, and thegas 50 in the two bearing gap elements 41 and 44 is subjected to acorrespondingly less centrifugal force during rotation of the rotorshaft 4 with the bearing inner part 5. This in turn means that, when thebearing inner part 5 is rotating on the rotor shaft 4, the density ofthe gas 50 which rotates with it in the bearing gap elements 41 and 44(as well as 42 and 43) which are closer to the axis is reduced, and thatin the bearing gap 10 which is further from the axis is greater. Since,on the other hand, the density of the gas 50 increases again since thetemperature decreases sharply toward the bearing gap 10, these twoeffects that act in opposite senses compensate for one another, to acertain extent. This embodiment of the magnetic bearing 3 thus resultsin a more homogeneous density distribution and more stable layering ofthe gas 50 within the magnetic bearing 3.

FIG. 4 shows a cross section through a modified form of a magneticbearing 2 for the device as illustrated in FIG. 1. The permanent-magnetelements on the outer bearing part, which is annotated 29, of themagnetic bearing 2 and a hollow-cylindrical, superconducting structure,which is annotated 32 and is fitted on the outside of the hollow shaft34, are now provided as the inner part 31. Furthermore, the permanentmagnets of the magnetic bearing 2 are not stacked axially, withpermanent-magnet elements 27 i, 27 j (where 1≦i≦j; 1≦j≦n) which areaxially extended and are in the form of segments of hollow cylindersbeing provided instead. The permanent-magnet elements 27 i, 27 j areeach spaced apart from one another via ferromagnetic elements 28 k(where1≦k≦2n), which are like strips and are likewise in the form of segmentsof hollow cylinders, and, together with them, form a closedhollow-cylindrical arrangement for the outer bearing part 29. Thefixed-position outer bearing part 29 surrounds the inner bearing part31, which can rotate, at a distance w which is defined by the gap widthw of the bearing gap 10. The hollow shaft 34 in turn surrounds the heattransmission body 35, forming the intermediate space 37 with the gapwidth x. The illustrated cross section clearly shows that both the gaps,which are arranged concentrically with one another, the bearing gap 10and the intermediate space 37, are each filled with the same gas 50.

FIG. 5 shows an embodiment of a device, modified from that shown in FIG.1, in which the heat transmission unit as shown in FIG. 1, which isformed from the heat transmission body 35 and the cold head 24, isreplaced by a heat transmission unit as shown in FIG. 5, which operateson the heat pipe principle. Working liquid 50′, which preferablycorresponds to the liquefied contact gas 50, is introduced into thecavity 30 via a preferably vacuum-insulated heat pipe 70 and via aninternal area 38′ which widens conically from the rear part of thehollow shaft 34 through the suspension element 48 to the cavity 30 inthe winding support 26. The heating results in the working liquid beingvaporized, and dissipates heat from the winding support 26 in the formof vaporization heat. The vaporized gas 50, which is used as the workinggas for the heat pipe 70, is transported on the opposite path throughthe internal area 38′ and through the heat pipe 70 to a condenser 71which is located outside the gastight wall 61, where it is cooled downvia the cold head 72 until it once again liquefies (condenses) to formthe working liquid 50′. The circuit (working cycle) in the heat pipe 70then commences once again. In this embodiment, the gas 50 is used notonly as a contact gas but also as a working gas for the cooling processby the heat pipe. A narrow intermediate gap 37′ is formed between theheat pipe 70 and the hollow shaft 34, is connected to the rest of thegas area 60, and allows mechanical decoupling between the heat pipe 70and rotating parts such as the hollow shaft 34.

For further details of the materials, configuration, dimensions andoperation of the magnetic bearings, in particular as shown in FIGS. 1 to5, reference shall be made to DE 44 36 831 C2, whose contents are alsoincluded in the disclosure of the present application.

The invention has been described in detail with particular reference topreferred embodiments thereof and examples, but it will be understoodthat variations and modifications can be effected within the spirit andscope of the invention.

What is claimed is:
 1. A device comprising: a rotor which is rotatableabout a rotation axis, the rotor having at least one superconductingwinding, which runs around the rotation axis; a magnetic bearing, tosupport the rotor in a contactless manner, the magnetic bearing having afixed position superconducting structure; a cooling device having a coldhead for indirect cooling of the superconducting structure of themagnetic bearing, the superconducting structure being cooled without aliquid cooling medium between the cold head and the superconductingstructure; and a gastight wall defining a common gas area, which atleast partially encloses the rotor and the magnetic bearing.
 2. Thedevice as claimed in claim 1, wherein the rotor has at least twomagnetic bearings, which are arranged on axially opposite sides of therotor with respect to the rotation axis.
 3. The device as claimed inclaim 1, wherein the rotor is supported by the magnetic bearing via arotor shaft connected to the rotor.
 4. The device as claimed in claim 3,wherein the rotor shaft passes through an opening in the gastight wall,and the opening in the gastight wall is sealed by a rotation seal. 5.The device as claimed in claim 1, wherein the winding is arranged in athermally conductive winding support, which has a cavity extendingaxially with respect to the rotation axis.
 6. The device as claimed inclaim 5, wherein the cavity in the winding support is connected to thecommon gas area in a manner which allows gas to be exchanged between thecavity and the common gas area.
 7. The device as claimed in claim 5further comprising a heat transmission unit thermally coupled to thewinding support, via a contact gas, the heat transmission unit beingthermally coupled to the cooling device.
 8. The device as claimed inclaim 7, wherein the heat transmission unit is mechanically decoupledfrom the rotor.
 9. The device as claimed in claim 8, wherein the rotorrotates with respect to the heat transmission unit.
 10. The device asclaimed in claim 7, wherein the heat transmission unit has a heattransmission body which projects into the cavity in the winding support,and an intermediate space between the heat transmission unit and thewinding support, is filled with a contact gas and is in fluidcommunication with the common gas area.
 11. The device as claimed inclaim 7, wherein the heat transmission unit dissipates heat from thewinding support by cyclic vaporization and condensation of a heattransport gas.
 12. The device as claimed in claim 5 wherein the cavityin the winding support is at least partially filled with the heattransport gas, the heat transmission unit dissipates heat from thewinding support by cyclic vaporization and condensation of a heattransport gas.
 13. The device as claimed in claim 1, wherein the rotoris supported by the magnetic bearing via a rotor shaft connected to therotor, the winding is arranged in a thermally conductive windingsupport, which has a cavity extending axially with respect to therotation axis, the device further comprise a heat transmission unitthermally coupled to the winding support, via a contact gas, the heattransmission unit being thermally coupled to the cooling device, therotor shaft is in the form of a hollow shaft, and the contact gas runsthrough the hollow shaft to thermally couple the heat transmission unitto the cooling device.
 14. The device as claimed in claim 1, wherein therotor has a gastight container which is evacuated, and the winding isarranged within the gastight container.
 15. The device as claimed inclaim 1, wherein the magnetic bearing comprises: at least one innerbearing part; at least one outer bearing part; and at least onepermanent magnet positioned on one of the two bearing parts such thatthe superconducting structure is positioned on the other of the twobearing parts, the permanent magnet and the superconducting structureinteracting with one another electromagnetically such that a bearinggap, which runs around the rotation axis, is maintained between theinner bearing part and the outer bearing part.
 16. The device as claimedin claim 15, wherein the rotor is supported on a rotor shaft, the innerbearing part is connected to the rotor shaft, and the outer bearing parthas the superconducting structure and is connected to the cold head. 17.The device as claimed in claim 15, wherein there are at least twomagnetic bearings, the bearing gap of each magnetic bearing is connectedto the common gas area at an axial end of the common gas area withrespect to the rotation axis.
 18. The device as claimed in claim 17,wherein the bearing gap is connected to the common gas area viaconnecting channels which are located closer to the rotation axis thanthe bearing gap.
 19. The device as claimed in claim 15, wherein themagnetic bearing has two or more permanent magnets, which are arrangedaxially with respect to the rotation axis.
 20. The device as claimed inclaim 19, wherein a flux concentrating element, which is at leastpartially formed of a magnetically permeable material, is arrangedbetween each of the two or more permanent magnets to guide the magneticflux of the permanent magnets.
 21. The device as claim 15, wherein themagnetic bearing has two or more permanent magnets, which are arrangedalongside one another in an arrangement which surrounds the rotationaxis.
 22. The device as claimed in claim 1, wherein the superconductorstructure has a superconductor having a critical temperature above 35 K.23. The device as claimed in claim 1, wherein the cooling device has acryogenic cooler system, which is thermally coupled to the cold head, tocool the superconducting structure of the magnetic bearing.
 24. Thedevice as claimed in claim 1, wherein the cold head extends from thesuperconducting structure to outside of the gastight wall, in adirection running essentially at a right angle to the rotation axis. 25.The device as claimed in claim 1, wherein the common gas area is filledwith an inert gas.
 26. The device as claimed in claim 25, wherein thecommon gas area contains substantially no water.
 27. The device asclaimed in claim 25, wherein the common gas area contains less than anamount of water sufficient to cause freezing.
 28. The device as claimedin claim 1, wherein the common gas area is at a pressure which is atleast as high as a gas pressure outside of the gastight wall.
 29. Thedevice as claimed in claim 1, wherein the superconductor structure has asuperconductor having a critical temperature above 77 K.
 30. The deviceas claimed in claim 1, wherein the common gas area is filled with atleast one of helium, neon or nitrogen.
 31. The device as claimed inclaim 1, wherein the common gas area is at atmosphere pressure or ahigher pressure.
 32. A device comprising: a rotor which is rotatableabout a rotation axis; a magnetic bearing, to support the rotor in acontactless manner, the magnetic bearing having a superconductingstructure; a cooling device having a cold head for cooling thesuperconducting structure of the magnetic bearing, the superconductingstructure being cooled without a liquid cooling medium between the coldhead and the superconducting structure; and a gastight wall defining acommon gas area, which at least partially encloses the rotor and themagnetic bearing.